1. Field of the Invention
The present invention relates to a piezoelectric component suitable for use in a filter of an electronic device, e.g., a mobile communication device such as a portable telephone, and also relates to a method of producing such a piezoelectric component.
2. Description of the Related Art
Recently, the sizes and weights of mobile communication devices such as automobile telephones and portable telephones have decreased, and the frequencies at which the devices are operated have been enhanced. In many cases, surface acoustic wave devices (piezoelectric components), which have small sizes and light weights, are used as filters mounted in these mobile communication devices. Especially, it is required to reduce the sizes and the weights of portable telephones. Accordingly, for electronic components to be mounted in such devices, it is also required to reduce the sizes and the weights thereof.
Surface acoustic wave devices utilize surface acoustic waves which are propagated along the piezoelectric substrates. Thus, it is necessary to protect the surface portions (functioning portions) of the devices, on which surface acoustic waves are propagated, from water, dust, and other similar contaminants. According to a conventional method of packaging a surface acoustic wave device, a surface acoustic wave element (piezoelectric element) is mounted onto a case-type package made of alumina or other suitable material by wire-bonding or flip chip bonding. Then, a cover (lid) made of a metal or ceramic is soldered to the package, and the package is air-tightly sealed by welding, soldering, or other similar sealing means, or by use of glass or suitable material.
However, according to the above-described packaging structure, if the sizes of the case-type packages onto which surface acoustic wave elements are mounted are not reduced, the sizes and the heights of surface acoustic wave devices cannot be reduced, even if the sizes of surface acoustic wave elements are reduced by the advanced techniques for fine wiring. Moreover, the expenditure of small-sized case-type packages is high. Therefore, surface acoustic wave devices to which chip size packages are applied using flip chip bonding used in the semiconductor component fields have been developed.
For example, a method is disclosed in Japanese Unexamined Patent Application Publication No. 8-204497 and in Japanese Unexamined Patent Application Publication No. 7-321583, in which plural surface acoustic wave elements, which are mounted on a mounting substrate by flip chip bonding, are sealed with a resin, and thereafter, the elements are diced into respective chips. This method is disadvantageous in that a liquid resin invades the surface acoustic wave propagation portion (functioning portion), and thereby, a deficient device which must be rejected is produced.
A countermeasure against the formation of such a rejected device has been disclosed in Japanese Unexamined Patent Application Publication No. 10-321666 in which a dam is provided on a surface acoustic wave element or a mounting substrate. However, when the velocity and the pressure at which the liquid resin is flowed into are varied and when the flowing-in speed of the liquid resin and the flowing-in pressure are increased, this countermeasure will be ineffective in solving the above-described problem. For this reason, a rejected device is formed, which is caused by the liquid resin invading the surface acoustic wave propagation area (vibrating portion, functioning portion) of the surface acoustic wave element. Moreover, air-bubbles are trapped in the liquid resin so that voids are formed. Thus, a sealing deficiency is caused. Moreover, the conventional method of forming a dam has problems in that the heights of the dams and the bumps may be different from each other, causing the adhesion strengths of the bumps to be reduced, and moreover, the formation of the dam increases the size of the surface acoustic wave element.
Moreover, conventional methods, in which a resin film is bonded to a surface acoustic wave element mounted by flip chip bonding so that the mounted element is sealed, and thereafter, the elements are diced into the respective chips, are disclosed, for example, in Japanese Unexamined Patent Application Publication No. 8-204497, International Patent Application Publication WO97/02596, Japanese Unexamined Patent Application Publication No. 2002-217221, Japanese Unexamined Patent Application Publication No. 2002-217523, Japanese Unexamined Patent Application Publication No. 2000-4139, Japanese Unexamined Patent Application Publication No. 2002-217219, and Japanese Unexamined Patent Application Publication No. 2002-217220. According to these conventional methods, for production of a surface acoustic wave device, a resin film is caused to adhere to the whole of the surface acoustic wave element by utilization of the flexibility of the resin film.
According to the above-described known techniques, inevitably, a resin film, which is thin and flexible, must be used for the above-described adhesion. Accordingly, in a finished device, an external impact tends to be applied directly to the surface acoustic wave element. As a result, the surface acoustic wave element is probably broken, or the bump is released by an impact caused when the device is mounted onto a user-side board. Moreover, various methods of bonding resin films have been disclosed. However, these methods have problems.
According to Japanese Unexamined Patent Application Publication No. 8-204497, a resin film is bonded to a mounting substrate by use of an adhesive or other similar material, as shown in FIG. 28. According to International Patent Application Publication WO97/02596, a resin film is heated to be deformed so that the film is bonded to a mounting substrate. However, because a hot-melted resin film is made to cover from the upper side, air-bubbles may be trapped by the resin film. Furthermore, the resin film may become substantially liquid, unless the melting of the resin film is properly controlled. Thus, the resin is in danger of flowing into a vibration space.
According to Japanese Unexamined Patent Application Publication No. 2002-217221 and Japanese Unexamined Patent Application Publication No. 2002-217523, a resin film is heated and pressed by a jig so that the resin film is bonded to a mounting substrate. However, according to these methods, it is necessary for the substrate and the film to have a large area in which they are heated and pressed for bonding the mounting substrate and the resin film to each other. Accordingly, it is difficult to produce a small-sized surface acoustic wave device. Moreover, the surface acoustic wave devices produced by the above-described methods are sealed with thin resin films. Thus, the air-tightness is insufficient.
According to Japanese Unexamined Patent Application Publication No. 2000-4139, the surface acoustic wave device sealed with a resin film is further sealed with a resin. However, this method is disadvantageous in reduction of the height of the device because the height is increased by the thickness of the resin in addition to that of the resin film.
According to Japanese Unexamined Patent Application Publication No. 2002-217219, a resin film is vacuum-formed. Further, according to Japanese Unexamined Patent Application Publication No. 2002-217220, a resin film is pre-formed so that no air-bubbles are formed. However, these methods have problems in that an exclusive-use apparatus is required for the processing, the number of processes is increased, and the manufacturing cost is high.
The above-described problems also occur in piezoelectric components such as piezoelectric resonators and piezoelectric filters in each of which piezoelectric resonators are arranged in a ladder configuration. The piezoelectric resonator contains a Si substrate having an opening or concavity and a vibration portion. The vibration portion is positioned to cover the opening or concavity and has a structure in which a pair of upper and lower electrodes in opposition to each other are placed on the upper and lower surfaces of a piezoelectric thin-film having at least one layer (e.g., made of ZnO and AlN) so that the thin film is sandwiched between the upper and lower electrodes.